There are many varieties of tide clock devices on the market and patented. These devices, whether mechanical or electrical, use a predetermined time period, typically twelve hours and twenty-five minutes, representing an average tidal cycle. The devices are then set by the user to the proper point in the current tidal cycle using local information or National Oceanic and Atmospheric Administration (NOAA) tide chart information. Examples of such devices may be found in U.S. Pat. Nos. 3,703,804, 4,035,167, 4,412,749, and 4,849,949.
The display incorporated in these devices takes many forms. Many display the time to or from high and low tide in hours and minutes. Others have a more graphic display that is indicative of the relative height of the water as opposed to the time to the next tidal event. Many of these displays use motor-driven discs that move by a viewing window to create a display that changes with time. Other devices use electronic displays such as bar graph displays to indicate the relative water height.
In reality, the tidal interval, or time between consecutive tides, differs between every tidal cycle. The tidal cycle difference causes such devices that use a constant interval to predict the next tidal occurrence to be in error by as much as plus or minus one hour. In addition, these devices can be set at a time when the actual tidal interval is in error from the average tidal interval, thereby causing additional error.
The height of each tidal occurrence is different. Devices that use a constant mechanism to display the height of the next tidal occurrence can be in error by as much as 50% of the relative height. In addition, these devices can be set at a time when the actual tidal height is in error from the average tidal height, thereby causing additional error in both the time of the next tidal occurrence and the relative height of the water.